Production of powdered metal

ABSTRACT

Miniaturized apparatus for producing powdered metal of exceptional purity and controlled particle size and shape. The atomizing tank is surmounted by a secondary gas chamber which separates the atomizing nozzle from the molten metal source. The molten metal stream falls through the secondary gas chamber and through the atomizing nozzle into the tank. High velocity gas from the nozzle atomizes the stream and creates a low pressure region within the tank. Gas from the secondary gas chamber passes through the nozzle along with the molten metal stream into the tank. The cooling effect of the high volume of gas permits use of a smaller atomizing tank than those used in prior art units.

United States Patent Jossick [541 PRODUCTION OF POWDERED METAL [72] Inventor: James L. Jossick, Newtown, Conn.

[73] Assignee: Conn. Engineering Assoc. Corp.,

Newtown, Conn.

[22] Filed: March 20, 1970 [21] App]. No.: 21,439

52 U.S.Cl ..42s/7,7s/0.5 C,264/12, 266/34 R 51 Int. Cl ..C21c 7/00 [58] Field of Search.266/34 R, 38; 18/25 R, 2.5 RR; 264/12, 18; 75/05 R, 0.5 C; 239/79, 82

[451 Oct. 3, 1972 3,253,783 5/ 1966 Probst et a1 ..239/82 FOREIGN PATENTS OR APPLICATIONS 461,125 11/1949 Canada ..18/2.5 R

Primary Examiner-Gerald A. Dost Attorney-Wooster, Davis and Cifelli ABSTRACT Miniaturized apparatus for producing powdered metal of exceptional purity and controlled particle size and shape. The atomizing tank is surmounted by a secondary gas chamber which separates the atomizing nozzle from the molten metal source. The molten metal stream falls through the secondary gas chamber and through the atomizing nozzle into the tank. High velocity gas from the nozzle atomizes the stream and creates a low pressure region within the tank. Gas from the secondary gas chamber passes through the nozzle along with the molten metal stream into the tank. The cooling effect of the high volume of gas permits use of a smaller atomizing tank than those used in prior art units.

10 Claims, 7 Drawing Figures PATENTEI] [1N3 I972 SHEET 1 BF 3' INVENTOR.

Pmmmwa m2 3,695,795

SHEET UF 3 INVENTOR.

HTT NFYS BACKGROUND OF THE INVENTION This invention relates to the production. of powdered metal and, more particularly, to miniaturized apparatus;

capable of producing powdered metal of exceptionally high quality.

The production of powdered metal by means of a nozzle for atomizing a molten metal stream is well known. More or less typical of the prior art are United States Pat. Nos. 2,968,062 and 3,253,783 of Probst et al. Typical prior art apparatus comprises a molten metal receptacle or crucible including an atomizing tip having arelatively long discharge passage. The atomizing tip extendsthrough the center ofa circular nozzle. The nozzle includes a conical opening which surrounds the end of the atomizingtip. High pressure gas from this opening atomizes the metal, which solidifies and drops into the receiving tank. Due to the very large amount of heat which must be dissipated, these. receiving tanks must be quite large.

Operation of these prior art units is quite hazardous. This is due to the fact that failure of the atomizing tip may permit a large volume of molten metal to drop into the tank, which is under pressure. Some of the molten metal may then be blown out of the tank, while the remainder often burns through the bottom of the tank.

Another disadvantage of prior art unitsarises from the long discharge passage in the atomizing tip. The molten metal tends to chill and freeze in this passage. Furthermore, there has been recent speculation that cryogenic atomization, usingcooled atomizing gas may result in powders having improved metallurgical properties. Such aprocess would be extremely difficult, if not impossible, in such prior art units.

SUMMARY OF THE INVENTION Apparatus for the production of powdered metal which comprises a tank including a top wall which defines an inlet opening. An atomizing nozzle is positioned adjacent the opening and means are provided for supplying pressurized gas to the nozzle. A gas chamber surrounds the nozzle and means are provided for supplying gas to this chamber. The molten metal streams through the chamber, the nozzle, and the opening into the tank.

BRIEF DESCRIPTION OF THE DRAWINGS.

The invention may be best understood by reference to the following description and the appended drawings wherein:

FIG. 1 is apartial top view of an atomizing tank in accordance with this invention;

FIG. 2 is an elevation, partially broken away, of the upper portion of the tank of FIG. ,1;

FIG. 3 is an enlarged partial cross sectiontaken substantially along the line 3--3 of FIG. 1;

FIG. 4 is an enlarged cross section of the nozzle taken substantially along the line 4--4 of FIG. 3;

FIG. 5 is a top view of the nozzle shown in FIG. 4, with a portion broken away to show its internal construction;

FIG. 6 is a perspective view of a portion of the nozzle of FIGS. 4 and 5; and

FIG. 7 is a schematic diagram of an installation for producing powdered metal.

DESCRIPTION OF THE PREFERRED EMBODIMENT With particular reference to FIGS. 1 and 2, there is illustrated the top of an atomizing tank 10 having a domed top 12 and a conical hopper bottom 14 (FIG. 7). The domed top defines a central opening 16. Mounted on top 12 is a cylindrical wall 18 having a horizontal upper flange 20 to which is bolted a top plate 22. The top 12, wall 18, and top plate 22 define a secondary gas chamber 24 which is an important feature of this invention. Feeding into chamber 24 are secondary gas supply lines 25a-c. Mounted on domed top 12 and surrounding opening 16 is an atomizing nozzle 26. The nozzle is connected to a source of high pressure gas through a supply line 28 terminating in a pair of U-shaped branch lines 30, 31 which supply the gas to opposite sides of the nozzle.

Referring now to FIG. 3, it will be noted that top plate 22 defines a central conical opening 32 in which is mounted a conical plug 34. Plug 34 defines a vertical opening 36 terminating in a circular recess at its top surface. Mounted in the opening 36 and suported in the recess by a circular flange 38 is an atomizing tip 40 of a suitable refractory material, such as soapstone or zirconia. A refractory disc 42 extends outwardly from flange 38 and is recessed to receive a metal plate 44 and a water cooled coil 46. Positioned atop the refractory disc 42 is the crucible 48of an induction furnace 50. Surrounding the crucible 48 is a water induction coil 52.

The atomizing tip 40 defines an upper recess 54 and a lower recess 56 joined by a short passage 58 of reduced diameter. During normal operation the upper recess 54 is filled with molten metal and passage 58 defines the metal stream. In order to support the weight of the molten metal, the top of recess 56 is arched as shown. The flow of molten metal may be controlled by a stopper rod 60 which may be inserted into the crucible and has arounded tip for closing passage 58.

The construction of atomizing nozzle 26 will now be described in detail with particular reference to FIGS. 4, 5 and 6. The nozzle comprises a cylindrical side wall 62 which has diametrically. opposed openings 64, 66 receiving the ends of branch lines 30, 31. Bolted to the bottom of side wall 62 is a base plate 68 which includes a raised central portion 70 fitting within the side wall 62. The lower surface is relieved as shown in FIG. 4 and the base plate defines a central circular aperture 72. Brazed or otherwise suitably secured to the raised portion 70 of the base plate, are four rectangular baffles 74, 76, 78, 80. The function of these baffles is to equalize the flow of high pressure gas entering the nozzle from lines 30, 31 and to impart a swirling motion thereto. To this end, they are angularly disposed as shown in FIGS. 5 and 6. Two larger baffles 74, 76 are positioned on one diameter and directly in the path of the entering gas. The smaller baffles 78, 80 are positioned on the diameter at right angles thereto. The baffies are ported so as not to prevent the circular flow of gas in the nozzle. Mounted on the top of side wall 62 is a top plate 82. The top plate 82 hasa central opening 84 from which depends a conical skirt 86. The skirt 86 extends through the aperture 72 but is spaced therefrom to define a circular discharge orifice.

A complete installation for the manufacture of powdered metal in accordance with this invention is illustrated schematically in FIG. 7. The system is totally enclosed and the gas employed is recirculated. Any suitable gas may be employed such as, for example helium, argon, or nitrogen or a blend of these or different gases. The gas is supplied from gas storage bottles 88 through a solenoid valve 90 controlled from a push bottom 92 or other suitable means. Pressure in the system is maintained at the desired level by means of a gasometer 94. In an exemplary installation, this pressure is maintained at a value of not more than two inches of water. A compressor 96 raises the gas pressure to approximately 100 pounds per square inch and supplies it through a receiving tank 98 to supply line 28 of the nozzle. This high pressure side of the system is provided with a high pressure relief 100 and the gas may be preheated or precooled by a heat exchanger 102, if desired. Gas leaves the atomizing tank through a discharge line 104 and a cyclone separator 106 for removing entrained powdered metal. Any remaining powder is removed by passing the gas through a coarse filter 108 and a fine filter 1 before returning it to compressor 96.

In the actual tank illustrated in FIGS. 1 and 2 there are illustrated three secondary gas lines a-c. To simplify the schematic, only lines 250 and 25b are illustrated. These lines are connected to receive gas from the atomizing tank through separators 112a, l12b having powder receptacles 1 14a, 1 14b.

To operate the system, the static gas pressure is maintained, as indicated above, at not more than 2 inches of water. The crucible 48 is filled with the metal to be powdered, the stopper rod 60 being in place as shown in FIG. 3. The induction coil 52 is then energized. The induction field heats and melts the metal in the crucible and its temperature is raised to approximately 200 to 300 degrees over its melting point. Compressor 96 is started and it supplies gas to nozzle 26 under a pressure of approximately 100 pounds per square inch and at a rate of approximately 150 cubic feet per minute. The gas strikes the baffle plates within the nozzle and is given a swirling motion and, at the same time, is forced downwardly through the aperture 72 in a cone shaped jet. The stopper rod 60 is removed, permitting the molten metal to flow in a narrow stream through passage 58 in atomizing tip 40. It should be noted that the atomizing tip is in the induction field of coil 52, thereby further reducing any tendency for the metal to freeze in the tip.

The molten stream flows through the secondary gas chamber 24 and through the central opening 84 of nozzle 26. Below the nozzle the metal is struck by the high velocity swirling gas stream which breaks it up and atomizes the metal, forming individual particles. The swirling nature of the gas stream gives the atomized particles a spinning effect resulting in more spherical particles. The particles are cooled quickly by virtue of the large volume of gas available. This large volume is due to the effect of the secondary gas chamber 24 in conjunction with nozzle 26. The high velocity jet of gas issuing from aperture 72 creates a region of lower pressure just below the nozzle. Accordingly, the secondary gas which fills chamber 24 is educted downwardly through the nozzle 26 with the molten stream. This gas is replaced by gas taken from the interior of the atomizing tank through the secondary gas lines 25a-c. Alternatively, this could also be taken directly from the gasometer or other portion of the gas system. This would have the advantage of insuring that the secondary gas would be cooler and more powder free.

The nozzle 26 may be made in such a manner that the protrusion of skirt 86 and the resulting size of the discharge orifice may be varied to give coarser or finer particles. Alternatively, different nozzles may be installed.

A number of advantages accrue from this invention. One such advantage is safety. In prior art devices, as previously described, failure of the molten metal feeding tip can result in a large volume of molten metal being forced into a pressurized tank, resulting in an explosive condition. However, in the invention this is prevented. If the atomizing tip 40 should fail, the large volume of secondary gas 24 will cause the metal to freeze to the tip and to the atomizing nozzle and prevent any significant amount of molten metal from dropping to the bottom of the atomizing tank and melting through the steel.

Another advantage is that the secondary gas chamber is free of powder as a result of its being separated from the atomizing chamber within the tank. This, accordingly, eliminates powder build up on the atomizing nozzle and atomizing tip.

As pointed out above, high temperatures are a severe problem in prior art atomizing tanks and the problem is usually overcome by increasing the size of the tank. Even so, prior art atomizing tanks may have temperatures as high as 800"F. However, due to the secondary gas chamber of this invention much greater volumes of gas are actually employed and, accordingly, the metal is more quickly and more efficiently quenched. As a result, the size of the atomizing tank may be drastically reduced. In an exemplary installation, for example, the tank is ten feet in height and five feet in diameter, and still the temperature does not exceed 500F even though 300 to 500 pounds of metal per hour are being atomized. The actual pressure within the tank itself is approximately 6 inches of water. In this installation the secondary gas is recirculated from the atomizing tank as shown in FIG. 7. The temperature would be even further reduced by supplying the secondary gas directly from, for example, the gasometer.

Still another advantage of the present invention is that higher purity metal may be produced as a result of the totally enclosed inert gas recirculation system. This also results in economies resulting from decreased gas loss.

It will be apparent to those skilled in the art that a number of variations and modifications may be made in this invention without departing from its spirit and scope. Accordingly, the foregoing description is to be construed as illustrative only, rather than limiting. This invention is limited only by the scope of the following claims.

What is claimed is:

1. Apparatus for the production of powdered metal which comprises: a tank including a top wall defining an inlet opening therein; an atomizing nozzle adjacent said opening; means for supplying pressurized gas to said nozzle; means forming a secondary gas chamber surrounding said nozzle; means for supplying pressurized gas to said secondary gas chamber; and means for streaming molten metal sequentially through said secondary gas chamber, nozzle, and opening into said tank.

2. The apparatus of claim 1 wherein said nozzle comprises: means defining a central opening encircling said streaming molten metal; and means defining a conical gas jet directed downwardly into said tank with its apex at said streaming molten metal.

3. The apparatus of claim 1 wherein said nozzle comprises: a substantially cylindrical outer wall; an inner wall spaced from, and concentric with, said outer wall and defining a vertical passage; an annular top wall interconnecting said outer and inner walls; and an annular bottom wall extending inwardly from said outer wall and defining an annular discharge orifice with said inner wall.

4. The apparatus of claim 3 wherein said inner wall is substantially conical.

5. The apparatus of claim 3 wherein angularly oriented baffles are disposed between said inner and outer walls.

6. The apparatus of claim 1 wherein said means for streaming comprises: a molten metal crucible; and a refractory tip in said crucible defining a molten metal discharge passage spaced above said nozzle.

7. The apparatus of claim 6 wherein said refractory tip defines a first recess communicating with said crucible and a second recess communicating with said secondary gas chamber, said discharge passage being formed therebetween and being short relative to the axial length of said recesses.

8. Apparatus for the production of powdered metal which comprises: a tank including a top wall defining an inlet opening therein; an annular atomizing nozzle surrounding said opening for defining a converging conical gas jet directed downwardly into said tank; means forming a secondary gas chamber surrounding said nozzle and communicating with said tank through said inlet opening; a molten metal crucible including a refractory tip defining a molten metal discharge passage, said crucible positioned atop said secondary gas chamber to direct molten metal from said discharge passage sequentially through said secondary gas chamber, nozzle, and opening into said tank; means for supplying pressurized gas at a first pressure to said secondary gas chamber; and means for supplying pressurized gas at a second, substantially higher, pressure to said nozzle.

9. Apparatus for the production of powdered metal which comprises: a tank including a top wall defining an inlet opening therein; an atomizing nozzle adjacent said opening; means for supplying pressurized gas to said nozzle; means forming a secondary gas chamber surrounding said nozzle; means for supplying gas to said secondary gas chamber including recirculating lines interconnecting said tank and said secondary gas chamber; and means for streaming molten metal sequentially through said secondary gas chamber, nozzle, and opening into said tank.

10. The apparatus of claim 6 wherein said crucible and refractory tip are mounted to said means forming a secondary chamber by a refractory disc positioned atop a metal plate and cooling coils. 

1. Apparatus for the production of powdered metal which comprises: a tank including a top wall defining an inlet opening therein; an atomizing nozzle adjacent said opening; means for supplying pressurized gas to said nozzle; means forming a secondary gas chamber surrounding said nozzle; means for supplying pressurized gas to said secondary gas chamber; and means for streaming molten metal sequentially through said secondary gas chamber, nozzle, and opening into said tank.
 2. The apparatus of claim 1 wherein said nozzle comprises: means defining a central opening encircling said streaming molten metal; and means defining a conical gas jet directed downwardly into said tank with its apex at said streaming molten metal.
 3. The apparatus of claim 1 wherein said nozzle comprises: a substantially cylindrical outer wall; an inner wall spaced from, and concentric with, said outer wall and defining a vertical passage; an annular top wall interconnecting said outer and inner walls; and an annular bottom wall extending inwardly from said outer wall and defining an annular discharge orifice with said inner wall.
 4. The apparatus of claim 3 wherein said inner wall is substantially conical.
 5. The apparatus of claim 3 wherein angularly oriented baffles are disposed between said inner and outer walls.
 6. The apparatus of claim 1 wherein said means for streaming comprises: a molten metal crucible; and a refractory tip in said crucible defining a molten metal discharge passage spaced above said nozzle.
 7. The apparatus of claim 6 wherein said refractory tip defines a first recess communicatiNg with said crucible and a second recess communicating with said secondary gas chamber, said discharge passage being formed therebetween and being short relative to the axial length of said recesses.
 8. Apparatus for the production of powdered metal which comprises: a tank including a top wall defining an inlet opening therein; an annular atomizing nozzle surrounding said opening for defining a converging conical gas jet directed downwardly into said tank; means forming a secondary gas chamber surrounding said nozzle and communicating with said tank through said inlet opening; a molten metal crucible including a refractory tip defining a molten metal discharge passage, said crucible positioned atop said secondary gas chamber to direct molten metal from said discharge passage sequentially through said secondary gas chamber, nozzle, and opening into said tank; means for supplying pressurized gas at a first pressure to said secondary gas chamber; and means for supplying pressurized gas at a second, substantially higher, pressure to said nozzle.
 9. Apparatus for the production of powdered metal which comprises: a tank including a top wall defining an inlet opening therein; an atomizing nozzle adjacent said opening; means for supplying pressurized gas to said nozzle; means forming a secondary gas chamber surrounding said nozzle; means for supplying gas to said secondary gas chamber including recirculating lines interconnecting said tank and said secondary gas chamber; and means for streaming molten metal sequentially through said secondary gas chamber, nozzle, and opening into said tank.
 10. The apparatus of claim 6 wherein said crucible and refractory tip are mounted to said means forming a secondary chamber by a refractory disc positioned atop a metal plate and cooling coils. 